coral need "nutrients", those are the nitrates and phosphates....too much is bad, not enough is bad. There's a sweet spot that your tank will settle into. Alkalinity also plays a part. If you are having Alk swings the euphyllia will shrivel and retract. All corals like stability. Your tank is pretty new and is probably lacking the "good stuffs" (bacteria, microfauna) that coral eat and keeps the system stable. Regular feeding of fish will keep nutrients in the system. Coral love fish poop. If you can find someone with a well established tank, try and bum a small piece of rock off them and add it to your tank. It'll go along way.
Beyond that is lighting. Euphyllia like moderate light. In my tank I keep my hammers at about 150-200 PAR. I have a toxic, bi-color, trojan frogspawn and a few torches. But I do keep my torches in higher light and flow.
Good testing and keeping a good log of what they are will go along way. Tanks at first are wild, they swing around and can have "bad days"....once they age out a bit (3-4 months) they'll start settling down. When you see your first signs of coralline is a good indicator that calcification is happening. That would show you that the euphyllia can grow by creating their "bone zones" (tubes).
